The present invention relates to a polyamide resin composition and its shaped article which have excellent properties such as a thermal resistance, a heating-cooling repeat resistance, a rigidity, a toughness, a road antifreezing agent resistance and so on.
Recently polyamide resins are applied to exterior parts of an automobile, for example, a cooling fan, a top and a base of radiator tank, a top and a base of heater core tank, a cylinder head cover, a canister, a gear, a connector, a valve, oil pans, a brake tube, a tube for fuel tubing and parts for exhaust gas, because the polyamide resins have excellent properties such as a heat resistance, an oil resistance, a moldability, a rigidity and a toughness, etc.
Higher polyamide resins represented by nylon 11 and nylon 12 among polyamide resins have not only good properties such as a toughness, dimensional stability and chemical agent resistance but also an excellent resistance to road antifreezing agents such as calcium chloride and magnesium chloride.
Therefore, they have aroused interest in using as materials for the exterior parts of automobile and have already been used as some specific functional parts.
The fact is, however, that an extension of application for the higher nylons is limited because of insufficient thermal resistance and rigidity in comparison with metals.
On the other hand, since polyamides having a comparatively high amide group concentration, such as nylon 6 and nylon 66, have high thermal resistance and high toughness and are inexpensive, they have been used as materials for exterior parts of an automobile. However, they are not necessarily satisfactory materials because they have defects that they have a high hydroscopicity and a poor dimensional stability, and that they are attacked by road antifreezing agents such as calcium chloride, magnesium chloride and crack.
It is known to compensate for polymer defects by mixing the lower polyamide such as nylon 6, nylon 66, etc. and the higher polyamide such as nylon 11, nylon 12, etc. (Japanese Pat. Application Kokai Publication Nos. 57-212252, 57-80448 and 57-80449).
The blends of the lower polyamide and the higher polyamide have a considerable supplemental effect on each other, but they also have a poor heat resistance because the higher polyamide has a lower melting point. Furthermore, the blends are insufficient in, the so called, "heat-cooling repeat resistance" and are insufficient in a resistance for calcium chloride under condition such as heating-cooling repeat.
Meanwhile, the experior parts of automobile require many excellent properties which must resist a high temperatures from the heat of the an engine, resistance to a heating-cooling repeat caused a radiator and must protect against cracking caused by halogenated metal such as calcium chloride which is spread on the road as a road antifreezing agent. The exterior parts must also possess excellent rigidity, toughness and dimensional stability.